Recently, as miniaturization, slimming, and high density of electronic devices have been emphasized, high integration and thinning of printed circuit boards included in electronic devices have been demanded. Printed circuit boards may be classified into a rigid printed circuit board, a flexible printed circuit board, a rigid-flex printed circuit board in which a rigid printed circuit board and a flexible printed circuit board are combined, and so on, based on the physical properties thereof.
Among them, the demand for flexible printed circuit boards (also referred to as “flexible printed circuits (FPCs)”) and rigid-flex printed circuit boards is increasing, and the printed circuit boards have a structure in which a circuit made of a metal layer is formed on an insulative film, such as a polyimide (PI) film.
As the high integration of circuits is required, a rigid-flex printed circuit board has a multilayer structure in which a double-sided printed circuit board and a single-sided printed circuit board are coupled to each other. That is, a multilayer rigid-flex printed circuit board may have a structure in which single-sided printed circuit boards, each of which includes a circuit layer and an insulating layer, are respectively bonded to the top and bottom sides of a double-sided printed circuit board, which includes a circuit layer and an insulating layer, via bonding sheets therebetween.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.